Still getting emails from collections department

I had a cellphone contract with Nashua Mobile and settled the account in 2012 received a paid up letter from them to my surprise now in 2015 im receiving telephone calls and emails from [Email Removed] I then contacted them and sent them the paid up letter ,i corresponded with the manager Sandile Maphosa asking him to send me confirmation that account is now updated and closed on their side but still im receiving these collection email, Im really frustrated as I have settled this account a long time ago with Nashua Mobile.